1. Field of the Invention
The present invention relates to a printing press with a temperature control unit for a plate cylinder and more particularly for a surface of each printing plate mounted on the plate cylinder.
2. Related Art
A printing press constructed having a plate cylinder on which printing plates are mounted is equipped with an ink unit for supplying ink onto each printing plate. The ink unit transfers ink from an ink fountain through a number of ink rollers, and finally onto the surface of each printing plate mounted on the plate cylinder through an ink-applying roller (a foam roller) of these ink rollers. As used throughout the description, by a surface of the plate cylinder or a plate surface is meant the circumference of the plate cylinder with a single or plural printing plates mounted thereon.
According to the above ink transferring operation, the viscosity of ink is influenced by the temperature. That is, when the plate surface has a relatively low temperature, ink has excessively high viscosity and hence is hard to transfer such as on an edge portion of an image to be printed. On the other hand, when the plate surface has a relatively high temperature, ink has excessively low viscosity and hence may cause blur such as in minute portions of an image printed on sheets of paper.
Thus, the amount of ink applied from the ink-applying roller onto the plate surface is greatly influenced by the temperature of the plate surface. In this regard, where the temperature control is made by a temperature control unit equipped on the ink-roller side for controlling the temperature of ink on the ink-roller side, this unit is still hard to allow ink transferred from the ink-applying roller onto the plate surface to be maintained in a good condition and hence hard to obtain a good quality of printing for the plate surface having a temperature out of a certain range. In order to address this problem, another approach was made as disclosed in Japanese Patent Laid-open No. HEI-8-1918.
In the above-cited reference, a temperature control unit has an air-feeding means having an air outlet fixed in position around the plate cylinder, through which air is fed onto the plate surface. This fixed arrangement of the air outlet causes a problem that the printing press tends to increase in size particularly for a portion around the plate cylinder. Specifically, the problem is that only a limited space is left for such an air outlet due to the necessity to locate various units and parts such as an ink unit, a blanket cylinder and the like around the plate cylinder. In some cases, the plate cylinder must be increased in size for accommodating the air outlet in addition to those units and cylinders.
An air outlet may be located away from the plate cylinder than the ink roller is, but an airflow from the air outlet may be blocked by the ink roller and therefore is hard to reach the plate surface, resulting in difficulty to precisely control the temperature of the plate surface.
In consideration of the above, it is an object of the present invention to provide a printing press with a temperature control unit for the plate surface of a plate cylinder that is capable of efficiently utilizing the space around the plate cylinder, while providing precise control of the temperature of the plate surface in easy manner.